As shown in FIG. 1, a conventional scrool compressor includes a fixed scroll 1, an orbiting scroll 2 and a frame 3, with the fixed scroll 1 being mounted on the frame 3 and including an end plate 1a, which has an inlet port 6 at its outer periphery and an outlet port 7 at its center, and an upstanding spiral wrap 1b on the end plate 1a. The orbiting scroll 2 includes an end plate 2a with an spiral having spiral wrap 2b, the same shape as that of the spiral wrap of the fixed scroll 1. An Oldham ring 5 and an eccentric portion of a main shaft 4 are arranged to engage with a rear surface of said orbiting scroll 2. The spiral wrap lb of the fixed scroll 1 and the spiral wrap 2b of the orbiting scroll 2 are arranged to be combined with each other, with their phases being shifted from each other. The main shaft 4 is rotatably supported by bearings 14b and 14c in the frame 3, and the eccentric portion 4a of the main shaft 4 engages with a boss 2c formed on the rear surface of the end plate 2a of the orbiting scroll 2, thereby driving the orbiting scroll 2. The Oldham ring is arranged to make reciprocal movement on the frame 3, on the one hand, and to make reciprocal movement relatively to the orbiting scroll member 2, on the other hand, thereby preventing the orbiting scroll 2 from rotating around its own axis. When the main shaft 4 is rotated, the orbiting scroll 2 causes an orbital movement, without causing rotation around its own axis, so that a gas suctioned into the compressor through the inlet port 6 is fed into a compression chamber 8. The compression chamber 8 gradually decreases its volume as the gas gradually moves to the central portion under the action of the orbital movement of the orbiting scroll 2. The gas confined in the compression chamber 8 gradually increases its pressure, until the gas is discharged from the outlet port 7 of the end plate la of the fixed scroll 1.
In the scroll type fluid machine of the above type, it is always required to maintain a sealing property between the wraps of the both scrolls and to make the finished shape and dimension of each scroll wrap at high precision. For this purpose, it has been a usual practice to form the scroll from metallic material such as Fe, A1 or the like and to apply machining process by a NC milling machine or the like. Such precision machining process requires relatively long time to make the scroll. There are further problems in the conventional scroll type fluid machine. That is, relatively little consideration has been heretofore given to a thermal environment surrounding the scroll type fluid machine and an influence of the thermal environment on the scroll type fluid machine, so that the problems such as superheating of the gas fed into the compressor or thermal deformation of the parts caused thereby remain unsolved. Particularly, in the case of the scroll compressor of high pressure case type, that is the scroll compressor in which the compressing element of the compressor is contained in a high pressure atmosphere (a discharged gas which is compressed to a high pressure) the gas suctioned into the compressor is heated to a higher temperature due to heat conducted through the fixed scroll 1, the frame 3 or the like, resulting in parts of the compressor becoming deformed due to uneven thermal distribution and pressure caused thereby. Thus, the satisfactory sealing property is lost and leakage of gas is increased, that adversely affect the performance of the compressor.
Furthermore, in the conventional scroll compressor it has been the usual practice to use the scrolls 1 and 2 made of metallic material. Accordingly, the sliding surfaces of these scrolls tend to produce wearing or sticking together to stop rotation during operation, so that the conventional scroll compressor lacks reliability. Particularly, when the scroll compressor is made in oil-free type, reduction of thermal expansion and thermal conduction and reduction of wearing on the sliding surfaces constitute severe and important problems in the scroll compressor.
Accordingly, in order to maintaining a high performance level for the scroll type fluid machine, it is necessary to maintain a proper gap between the constituting parts of the scroll type fluid machine for a long time in order to secure its good sealing property and to secure durability of sliding surfaces of the constituting parts.
Japanese Patent Application Laid-Open Sho 58-214689 proposes a construction of a scroll type fluid machine of a non-metallic material or ceramics, such as alumina (A1.sub.2 O.sub.3)-system oxides, silicon carbide (SiC)-system carbides, silicon nitride (Si.sub.3 N.sub.4)-system or boron nitride (BN)-system nitrides which have been subjected to heat treatment at high temperatures. This construction enables a suppression of the deformation of the parts caused by heat produced by compression, to control and maintain a proper gap between the parts, to decrease thermal conduction and to improve reliability of the sliding parts.
The construction proposed in the above-mentioned Japanese application still has some problems to be solved. That is, no consideration is given to formability of ceramics, maintaining of precision of product of ceramics and lubricant oil holding property at relatively sliding parts and, consequently, problems concerning the number of machining steps and the reliability of the product remain unsolved. In other words, in case of the conventional ceramics as described above, an art for producing ceramics having uniform characteristic has not yet been established and, therefore, the ceramics produced by the conventional process lacks reliability. Furthermore, in the case of the conventional ceramics, relatively large dimensional change, such as of 15-20 %, is caused before and after a sintering process effected at a high temperature, and a product having a high dimensional precision cannot be formed, without applying a number of processing steps, such as grinding and finishing steps after effecting the high temperature processing. Accordingly, the manufacturing cost is very high. Furthermore, the ceramics, after being subjected to the high temperature processing has a structure in which the ceramic particles are diffused with respect to each other so as to fill up pores between the ceramic particles to form a dense structure and then sintered under such condition. Accordingly, the structure of the conventional ceramics is inferior in its pore distribution, its density and lubricant oil holding capability and, consequently, its lubricating property. Under such circumstances, the ceramics as described above has been not yet brought into practical use.